With the recent remarkable progress in computer-related technology there have been, year by year, advancements in the integration of LSI devices, while the memory capacities of magnetic disks are constantly on the increase; one of the fundamental techniques on which this progress has been based is polishing processing.
In manufacturing processes for LSI devices, polishing techniques for interlayer insulating films have been introduced and are beginning to be employed in practice for the major object of alleviating the problem on depth of focus in the photolithography step that occurs with refinement of design rules. There are also being seen more and more applications of polishing processing techniques such as embedded metal polishing (the Damascene method) for formation of fine wiring and the Shallow Trench Isolation method aimed at achieving separation of elements on narrower surface areas than by the conventional LOCOS (Local Oxidation of Silicon) method, as indispensable elemental technologies for the manufacture of next generation LSI devices. In this field, which involves polishing to miniature elements and wiring structures, high accuracy of finished surfaces is of course a requirement, but high efficiency and stability of the polishing process is also desired.
Polishing interlayer insulating film and Shallow Trench Isolation have been primarily studied using a slurry suspended silicon dioxide fine powder obtained by a gas phase method in an alkaline aqueous solution or a slurry suspended cerium oxide powder in water, whereas metal polishing has been primarily studied using a slurry suspended silicon dioxide powder, also obtained by a gas phase method, or aluminum oxide powder in water, with addition of an oxidizing agent such as iron nitrate or hydrogen peroxide. However, it has not yet been possible to achieve a level which satisfies all of the standpoints of surface-accuracy (or finishing level), polishing rate and stability of polishing rate. In order to achieve a high surface-accuracy it is necessary for the polishing-material particles to have a fineness on the order of submicrons, but smaller polishing-material particles generally result in a slower polishing rate. Thus, there has been a trade-off between surface-accuracy and polishing rate, and it has not generally been easy to achieve both.
Alkaline slurries suspended silicon dioxide fine powders have been used to achieve high surface-accuracy in polishing interlayer insulating film, which has been the most practiced method of polishing for LSI device manufacturing processes, but the low polishing rate has been an inconvenience. The polishing rate generally increases gradually from the start of polishing, tending to stabilize after the course of a given time of usually a few minutes or more; however, since the machining thickness is at most about 1 .mu.m for polishing in LSI device manufacturing processes, the polishing time most often is on the order of a few minutes. In other words, since the polishing is completed within a start-up region wherein polishing rate is still unstable, a considerable burden has existed in detecting the end point.
In contrast, cerium oxide slurries are advantageous for achieving both surface-accuracy and polishing rate in polishing interlayer insulating film and Shallow Trench Isolation method, but the polishing rate tends to increase with longer polishing time as in the case of silica slurries, and since the higher polishing rate makes it more difficult to detect the end point, this has constituted an obstacle against their practical implementation.
In the Shallow Trench Isolation method, a silicon nitride film is situated under the silicon dioxide film to be polished so that polishing is carried out with the silicon nitride film as a stopper, and therefore it has been necessary to have a fast polishing rate for the silicon dioxide film and a slow polishing rate for the silicon nitride film, or in other words, to have a high "selectivity ratio" which is the value of the polishing rate for the silicon dioxide film divided by that for the silicon nitride film; however, a problem has existed in that both silicon dioxide slurries and cerium oxide slurries have "selectivity ratios" of as low as about 2-6.
As explained above under "Background Art", it has been strongly desired to realize higher levels of both surface-accuracy and polishing rate, as well as stability of polishing rate, than is currently achieved in polishing steps on insulating films such as silicon dioxide films, silicon nitride films and organic films in manufacturing processes for LSI devices.
The present invention provides a polishing-material composition that can overcome the problems referred to above.